1. Field of the Invention
This invention relates generally to glass feeder plungers and operating mechanism therefor. In particular, this invention relates to an apparatus for effecting the cyclically reciprocating motion of glass feeder plungers according to selectable predetermined motion profiles.
2. Description of the Prior Art
Glass feeder plungers operate in cooperation with shears and other components of glass feeders in order to control the manner in which molten glass is delivered to glassware forming equipment downstream of the feeder. A glass feeder may include one or more plungers, each axially aligned above an associated orifice in the bottom of the feeder bowl through which emanates a molten glass stream. Each plunger (and orifice) has associated with it a pair of shears, and all plungers and shears are synchronized with the glassware forming machine and operate cyclically in order to cut the respective stream into predetermined gobs of molten glass. Each plunger serves to control the speed with which the glass emanates from its associated orifice. Consequently, the cyclical motion of each plunger must be controlled in a predetermined manner in order to achieve desired gob shapes and weights. Plunger motion (velocity) profiles are dependent upon many variables including glass temperature and type, machine speed, the type and size of glassware to be produced, etc. Consequently, even with job changes, minor alterations of plunger motion profile are desirable to maintain optimum machine operation and speed. In addition to the motion profile of each plunger, adjustments of the plunger differential (i.e. phase relationship of plunger cam to shear cut), stroke length and height (i.e. defined as the lowest point of the plunger tip above orifice) also affect gob formation. Glass feeder plunger operating mechanisms often comprise one or more feeder plungers carried by a lateral support bracket that is cantilevered from a moveable vertical support shaft. The plungers of such prior art feeders are operated by mechanical mechanisms and driven by an assembly of levers and links from a rotating cam, the profile of which serves to effect the desired plunger motion profile. Changes in plunger motion profiles are obviously very difficult since they require replacement of the cam. Additionally, adjustments of plunger differential, stroke length and height are made very complex because of the need to adjust the array of levers and links (see for example U.S. Pat. No. 2,725,681).
Reference to several patents is helpful in order to describe the representative state of prior art plunger operating mechanisms. U.S. Pat. No. 2,725,681 discloses the use of a hydraulic servo motor operatively connected with the vertically operated plunger assembly to assist the cam in effecting reciprocating vertical plunger motion. The use of the hydraulic servo-motor is desirable because of the considerable weight of some feeder plungers. For example, feeder plungers may vary in size from approximately 2 to 71/2" and in weight from 10 to 85 or more pounds. Because of the weight to be supported and moved vertically the components of the plunger operating mechanism must be strong enough to be suitable for the largest and heaviest plunger to be used in a particular feeder. This necessitates a continually heavy load on the feeder cam and on the cam driver (generally an electric motor).
U.S. Pat. No. 2,950,571 discloses the use of a hydraulic motor directly connected in line to the vertical shaft supporting a plunger. The hydraulic motor is responsive to signals from an electromechanical transducer which is provided to sense the plunger position. While the electromechanical transducer used in this system produces varying outputs representative of differently shaped cams, the apparatus is not capable of easily and repeatedly reproducing selected cam profiles. The various wave forms simulating various cam profiles are produced by varying the phase of the harmonic motion of synchro transducers used in this system. The manual adjustment of a complex array of gears varies this phase. The system disclosed in this patent is operated from a synchro transmitter connected to the output shaft of the electric motor which drives the glassware forming machine itself. The output of the synchro transmitter is connected to a mechanism box which produces electrical signals to activate the hydraulic motor via an electrically actuated hydraulic plunger valve. These signals are responsive to feedback from the electromechanical transducer.
U.S. Pat. No. 4,382,810 discloses a programmable timing controller for synchronizing the operation of one or more sections of a glassware forming machine with one another and with machine components common to all sections. The controller provides drive signals to an electro-hydraulic stepper motor common to both a gob feeder plunger mechanism and a conveyor and connected to each via respective gear reducers. The relative speeds of the plunger and conveyor mechanisms are fixed and established by the gear ratios. The pulse repetition rate of the drive signal is predetermined or controlled by an operator via a computerized speed control. This patent merely discloses one way of synchronizing plunger operation to that of other IS machine components and does not address the aforementioned problems associated with prior art plunger operating mechanisms.
U.S. Pat. No. 3,502,457 discloses a system for controlling the width of a glass ribbon emanating from a forehearth. A regulator or needle is aligned above the orifice and the height of the needle is adjusted as a function of the output of sensors used to detect ribbon width. The regulator is suspended from a block mounted to slide within vertical trackways and the block is in threaded engagement with a threaded shaft connected to a reversible stepping motor. Rotation of the motor in a selected direction raises or lowers the regulator accordingly. While this patent bears a superficial similarity to the invention disclosed herein it is noted that the device shown in this patent is not suitable for rapid, cyclical operation of a glass feeder plunger according to a selected velocity ormotion profile.
An additional disadvantage associated with prior art feeder plunger operating mechanisms is that their basically mechanical construction requires an operator to make many necessary adjustments directly at the location of the mechanism, right above the feeder bowl containing molten glass. In addition to the obvious hazard to the operator there is the risk that tools may be dropped into the feeder causing significant damage downstream.
Also, many prior art feeder plunger mechanisms rely on gravity to bring the plungers down, thus limiting machine speed since the plungers must follow the cam profile.
In view of the deficiencies of the prior art systems it is an object of this invention to provide a programmable control system and feeder plunger operating mechanism to facilitate use of preprogrammed plunger motion profiles.
It is another object of this invention to provide a feeder plunger operating mechanism wherein the plunger motion profile may be altered during plunger operation.
It is yet another object of this invention to provide a feeder plunger operating mechanism wherein the plunger height, stroke and differential may be adjusted remotely and during plunger operation.
It is still another object of this invention to provide a feeder plunger operating mechanism wherein the plungers are positively driven in both directions by a reversible electric motor.